Switch Trials Research Articles

Do tasks matter in task switching? Dissociating domain-general from context-specific brain activity

Throughout the past decade, the task-switching paradigm has been used extensively as a tool to delineate the neural mechanisms underlying flexible and goal-directed action control. Yet, given a large number of experimental procedures, the task-switching literature has yielded considerable inconsistencies calling for a systematic evaluation of the impact of methodological parameters. In the present study, we examine a fundamental and implicit assumption that has guided previous research on task switching. Does switch-related brain activation (i.e., the contrast between preparatory activity on switch versus repetition trials) reflect abstract cognitive control processes that are independent of specific task demands, and thus equivalent across different types of tasks? To answer this question, we compared the data of two fMRI studies that examined updating of task goals and/or stimulus–response mappings under almost identical protocols, but using entirely different tasks. In line with an abstract control process view, our results show that the vast majority of switch-related brain activity is insensitive to the context in which it occurs. The only region that exhibited a reliable contextual modulation was the anterior cingulate cortex, indicating that its contribution to preparatory adjustments might be linked to specific task demands.

A method for investigating age-related differences in the functional connectivity of cognitive control networks associated with dimensional change card sort performance.

The ability to adjust behavior to sudden changes in the environment develops gradually in childhood and adolescence. For example, in the Dimensional Change Card Sort task, participants switch from sorting cards one way, such as shape, to sorting them a different way, such as color. Adjusting behavior in this way exacts a small performance cost, or switch cost, such that responses are typically slower and more error-prone on switch trials in which the sorting rule changes as compared to repeat trials in which the sorting rule remains the same. The ability to flexibly adjust behavior is often said to develop gradually, in part because behavioral costs such as switch costs typically decrease with increasing age. Why aspects of higher-order cognition, such as behavioral flexibility, develop so gradually remains an open question. One hypothesis is that these changes occur in association with functional changes in broad-scale cognitive control networks. On this view, complex mental operations, such as switching, involve rapid interactions between several distributed brain regions, including those that update and maintain task rules, re-orient attention, and select behaviors. With development, functional connections between these regions strengthen, leading to faster and more efficient switching operations. The current video describes a method of testing this hypothesis through the collection and multivariate analysis of fMRI data from participants of different ages.

A Method for Investigating Age-related Differences in the Functional Connectivity of Cognitive Control Networks Associated with Dimensional Change Card Sort Performance

The ability to adjust behavior to sudden changes in the environment develops gradually in childhood and adolescence. For example, in the Dimensional Change Card Sort task, participants switch from sorting cards one way, such as shape, to sorting them a different way, such as color. Adjusting behavior in this way exacts a small performance cost, or switch cost, such that responses are typically slower and more error-prone on switch trials in which the sorting rule changes as compared to repeat trials in which the sorting rule remains the same. The ability to flexibly adjust behavior is often said to develop gradually, in part because behavioral costs such as switch costs typically decrease with increasing age. Why aspects of higher-order cognition, such as behavioral flexibility, develop so gradually remains an open question. One hypothesis is that these changes occur in association with functional changes in broad-scale cognitive control networks. On this view, complex mental operations, such as switching, involve rapid interactions between several distributed brain regions, including those that update and maintain task rules, re-orient attention, and select behaviors. With development, functional connections between these regions strengthen, leading to faster and more efficient switching operations. The current video describes a method of testing this hypothesis through the collection and multivariate analysis of fMRI data from participants of different ages.

Dissociating strategy-dependent and independent components in task preparation

A central aspect of cognitive control is the capacity to anticipatorily prepare for specific task requirements prior to carrying out a task. To study the changes caused by task preparation, the cued task-switching paradigm has generally been used. While research on anticipatory control has long focused on general processing differences between switch and repeat trials, more recent research suggests that contextual variations strongly modulate such differences. In the current paper, we argue that anticipatory task set preparation strongly depends on contextual variables leading to different strategies to prepare for an upcoming task. We provide behavioral as well as neuroscientific evidence for this claim. Furthermore, we show that some preparatory processes are sensitive to strategic modulations whereas other preparatory processes are not. Based on this, we propose a functional dissociation within the fronto-parietal network involved in task preparation.

Differential contribution of task conflicts to task switch cost and task mixing cost in alternating runs and cued task-switching: evidence from ex-Gaussian modeling of reaction time distributions.

Task switching involves switch cost (poorer performance switch trials than in task-repetition trials) and mixing cost (poorer performance in task-repetition trials than in trials from blocks without task switching). These are mainly studied with the alternating runs task-switching (ARTS) paradigm (in which the task changes every constant number of trials) or the cued task-switching (CTS) paradigm, in which the tasks change randomly. The authors tested the hypothesis that dealing with actual or potential conflicts regarding which task is currently required contribute to mixing cost in CTS more than in ARTS and contribute to switch costs more in ARTS than in CTS. This hypothesis was tested using ex-Gaussian modeling of reaction time (RT) distributions, in which the heaviness of the right tail marks task conflicts (Steinhauser and Hübner in J Exp Psychol Human Percept Perform 35:1398-1412 2009). As predicted, a heavier RT-distribution tail marked switch cost more strongly in ARTS than in CTS and marked mixing costs more strongly in CTS than in ARTS. These results indicate that switch cost and mixing cost reflect different processes in different task-switching paradigms.

Throwing out the rules: anticipatory alpha‐band oscillatory attention mechanisms during task‐set reconfigurations

We assessed the role of alpha-band oscillatory activity during a task-switching design that required participants to switch between an auditory and a visual task, while task-relevant audiovisual inputs were simultaneously presented. Instructional cues informed participants which task to perform on a given trial and we assessed alpha-band power in the short 1.35-s period intervening between the cue and the task-imperative stimuli, on the premise that attentional biasing mechanisms would be deployed to resolve competition between the auditory and visual inputs. Prior work had shown that alpha-band activity was differentially deployed depending on the modality of the cued task. Here, we asked whether this activity would, in turn, be differentially deployed depending on whether participants had just made a switch of task or were being asked to simply repeat the task. It is well established that performance speed and accuracy are poorer on switch than on repeat trials. Here, however, the use of instructional cues completely mitigated these classic switch-costs. Measures of alpha-band synchronisation and desynchronisation showed that there was indeed greater and earlier differential deployment of alpha-band activity on switch vs. repeat trials. Contrary to our hypothesis, this differential effect was entirely due to changes in the amount of desynchronisation observed during switch and repeat trials of the visual task, with more desynchronisation over both posterior and frontal scalp regions during switch-visual trials. These data imply that particularly vigorous, and essentially fully effective, anticipatory biasing mechanisms resolved the competition between competing auditory and visual inputs when a rapid switch of task was required.

Relating individual differences in internalizing symptoms to emotional attention set-shifting in children

A growing body of evidence points to links between internalizing symptoms and various executive functioning deficits, and especially to inhibition and set-shifting difficulties. However, there is limited developmental research regarding the impact of internalizing symptoms on the shifting function, particularly during middle childhood. The current study investigated attention shifting in a sample of 108 early school age children (7–11 years) using a task-switching paradigm which required participants to alternate between emotional and nonemotional judgments. Results indicated that higher levels of internalizing symptoms (anxiety and depression) had a detrimental effect on performance efficiency (measured by response times) but not on response accuracy. This effect was only observed on emotional (and not on nonemotional) repetition trials and did not affect switching trials; moreover, it was only present when feedback was presented to participants. The findings partially support the predictions of the Attentional Control Theory in a developmental sample and suggest that individual differences in internalizing symptoms play a role in children's ability to flexibly alternate between emotional judgments.

The association between fasting hypoglycemia and methylated mercaptopurine metabolites in children with acute lymphoblastic leukemia

Symptomatic fasting hypoglycemia has been reported as an unusual side effect in patients with acute lymphoblastic leukemia (ALL) on maintenance therapy. We evaluated the relation of the red cell 6-mercaptopurine (6-MP) metabolite 6-methyl-mercaptopurine (6MMP) with hypoglycemia. We retrospectively reviewed charts of three patients with ALL and symptomatic hypoglycemia while fasting who were noted to have high levels of 6MMP. All patients had an empiric trial of switching from evening to morning 6-MP administration, and two patients were subsequently switched to twice daily dosing. Patients also received complex carbohydrates at bedtime. Switching 6-MP from evening to morning administration reduced 6MMP levels yet preserved adequate levels of the active metabolite red cell 6-thioguanine nucleotide (6TGN). All patients had decreased hypoglycemic events when changed from evening to morning dosing. Two patients showed a rebound in 6MMP levels with return of hypoglycemic symptoms. Both were then switched to twice daily 6-MP dosing with one having a decrease in 6MMP and hypoglycemic symptoms. High levels of 6MMP are associated with symptomatic hypoglycemia which may be mitigated by switching to morning or twice daily 6-MP dose administration.

Attentional inertia and delayed orienting of spatial attention in task-switching.

Among the potential, but neglected, sources of task-switch costs is the need to reallocate attention to different attributes or objects. Even theorists who recognize the importance of attentional resetting in task-switching sometimes think it too efficient to result in significant behavioral costs. We examined the dynamics of spatial attention in a task-cuing paradigm using eye-tracking. Digits appeared simultaneously at 3 locations. A cue preceded this display by a variable interval, instructing the performance of 1 of 3 classification tasks (odd-even, low-high, inner-outer) each consistently associated with a location, so that task preparation could be tracked via fixation of the task-relevant location. Task-switching led to a delay in selecting the relevant location and a tendency to misallocate attention; the previously relevant location attracted attention much more than the other irrelevant location on switch trials, indicating "inertia" in attentional parameters rather than mere distractibility. These effects predicted reaction time switch costs within and over participants. The switch-induced delay was not confined to trials with slow/late orienting, but characteristic of most switch trials. The attentional pull of the previously relevant location was substantially reduced, but not eliminated, by extending the preparation interval to more than 1 sec, suggesting that attentional inertia contributes to the "residual" switch cost. A control condition, using identical displays but only 1 task, showed that these effects could not be attributed to the (small and transient) delays or inertia observed when the required orientation changed between trials in the absence of a task change.

Etravirine as a Switching Option for Patients with HIV RNA Suppression: A Review of Recent Trials

Unlike other nonnucleoside reverse transcriptase inhibitors, etravirine is only approved for use in treatment-experienced patients. In the DUET 1 and 2 trials, 1203 highly treatment-experienced patients were randomized to etravirine or placebo, in combination with darunavir/ritonavir and optimized background treatment. In these trials, etravirine showed significantly higher rates of HIV RNA suppression when compared with placebo (61% versus 40% at Week 48). There was no significant rise of lipids or neuropsychiatric adverse events, but there was an increase in the risk of rash with etravirine treatment. In the SENSE trial, which evaluated etravirine and efavirenz in 157 treatment-naïve patients in combination with 2 nucleoside analogues, there was a lower risk of lipid elevations and neuropsychiatric adverse events with etravirine when compared to efavirenz. Etravirine has been evaluated in three randomized switching studies. In the SSAT029 switch trial, 38 patients who had neuropsychiatric adverse events possibly related to efavirenz showed an improvement in these after switching to etravirine. The Swiss Switch-EE recruited 58 individuals without neuropsychiatric adverse events who were receiving efavirenz, and no benefit was shown when switching to etravirine. In the Spanish ETRA-SWITCH trial (n = 46), there were improvements in lipids when individuals switched from a protease inhibitor to etravirine. These switching trials were conducted in patients with full HIV RNA suppression: <50 copies/mL and with no history of virological failure or resistance to therapy. The results from these three randomized switching studies suggest a possible new role for etravirine, in combination with two nucleoside analogues, as a switching option for those with HIV RNA suppression but who are reporting adverse events possibly related to antiretroviral therapy. However a large well-powered trial would need to be conducted to strengthen the evidence from the pilot studies conducted so far.

Why the processing of repeated targets are better than that of no repetition: evidence from easy-to-difficult and difficult-to-easy switching situations

BackgroundPrevious studies have found that the processing of repeated targets are easier than that of non-repetition. Although several theories attempt to explain this issue, the underlying mechanism still remains uncovered. In this study, we tried to address this issue by exploring the underlying brain responses during this process.MethodsBrain activities were recorded while thirty participants performing a Stroop task (Chinese version) in the MRI scanner. Using pseudo-random strategies, we created two types of switching conditions (easy-to-difficult; difficult-to-easy) and relevant repeating conditions.ResultsThe results show that, in difficult-to-easy switching situation, higher brain activations are found in left precuneus than repeating ones (the precuneus is thought related with attention demands). In easy-to-difficult switching conditions, higher brain activations are found in precuneus, superior temporal gyrus, posterior cingulate cortex, and inferior frontal gyrus than repeating trials (most of these regions are thought related with executive function). No overlapping brain regions are observed in con_CON and incon_INCON conditions. Beta figures of the survived clusters in different conditions, correlations between brain activations and switch cost were calculated.ConclusionsThe present study suggests that the feature that response time in switching trials are longer than that in repeating trials are caused by the extra endeavors engaged in the switching processes.

Alpha activity reflects individual abilities to adapt to the environment

Recent findings suggest that oscillatory alpha activity (7–13Hz) is associated with functional inhibition of sensory regions by filtering incoming information. Accordingly the alpha power in visual regions varies in anticipation of upcoming, predictable stimuli which has consequences for visual processing and subsequent behavior. In covert spatial attention studies it has been demonstrated that performance correlates with the adaptation of alpha power in response to explicit spatial cueing. However it remains unknown whether such an adaptation also occurs in response to implicit statistical properties of a task. In a covert attention switching paradigm, we here show evidence that individuals differ on how they adapt to implicit statistical properties of the task. Subjects whose behavioral performance reflects the implicit change in switch trial likelihood show strong adjustment of anticipatory alpha power lateralization. Most importantly, the stronger the behavioral adjustment to the switch trial likelihood was, the stronger the adjustment of anticipatory posterior alpha lateralization. We conclude that anticipatory spatial attention is reflected in the distribution of posterior alpha band power which is predictive of individual detection performance in response to the implicit statistical properties of the task.

Task switching among two or four tasks: effects of a short-term variation of the number of candidate tasks

In two experiments, using a modified task-cueing paradigm, participants switched among a set of four tasks that was on some trials reduced to two by a pre-cue preceding the task cue. A pre-cue temporarily restricting the options to two candidate tasks facilitated performance on switch trials to a much larger extent than on repeat trials. This observation is interpreted as an indication of a short-term restructuring of a global task representation by implementing antagonistic constraints among the representations of the two remaining candidate tasks.

The prelimbic cortex and subthalamic nucleus contribute to cue-guided behavioral switching

Frontal cortex–basal ganglia circuitry supports behavioral switching when a change in outcome information is used to adapt response patterns. Less is known about whether specific frontal cortex–basal ganglia circuitry supports behavioral switching when cues signal that a change in response patterns should occur. The present experiments investigated whether the prelimbic cortex and subthalamic nucleus in male Long-Evans rats supports cue-guided switching in a conditional discrimination test. Rats learned in a cross-maze that a start arm cue (black or white) signaled which of two maze arms to enter for a food reward. The cue was switched every 3–6 trials. Baclofen and muscimol infused into the prelimbic cortex significantly impaired performance by increasing switch trial errors, as well as trials immediately following a switch trial (perseveration) and after initially making a correct switch (maintenance error). NMDA receptor blockade in the subthalamic nucleus significantly impaired performance by increasing switch errors and perseveration. Contralateral disconnection of these areas significantly reduced conditional discrimination performance by increasing switch and perseverative errors. These findings suggest that the prelimbic area and subthalamic nucleus support the use of cue information to facilitate an initial switch away from a previously relevant response pattern.

Postural inflexibility in PD: Does it affect compensatory stepping?

Parkinson's disease (PD) impairs the ability to shape postural responses to contextual factors. It is unknown whether such inflexibility pertains to compensatory steps to overcome balance perturbations. Participants were instructed to recover balance in response to a platform translation. A step was necessary to recover balance when the translation was large, whereas a feet-in-place (FiP) response was sufficient when the translation was small (i.e. no step). We compared step trials that required a switch away from the current postural set (switch trials: step trials that were preceded by FiP trials) with non-switch trials (i.e. step trials were preceded by identical step trials). 51 PD patients (59±7 years) were compared with 22 healthy controls (60±6 years). In a second analysis, we compared a subgroup of 14 freezers (PD-FOG) with a subgroup of 14 non-freezers (PD-noFOG; matched for age, gender and disease severity). Compared to non-switch trials, switch trials resulted in poorer step execution and more steps needed to recover balance. These switching effects were similar in PD patients and controls, and in PD-FOG and PD-noFOG patients. Overall, PD patients demonstrated poorer stepping performance than controls. PD-FOG had a worse performance than PD-noFOG. Moreover, PD patients, and particularly PD-FOG patients, were less able to improve step performance with repetitive step trials, in contrast to controls. Thus, there was no PD-related deficit to switch to an alternative response strategy, neither in patients with FOG nor in patients without FOG. Difficulty to adapt the step trial-by-trial might have contributed to the absence of switch deficits in PD.

Factor structure and validation of the attentional control scale

The Attentional Control Scale (ACS; Derryberry & Reed, 2002) has been used to assess executive control over attention in numerous studies, but no published data have examined the factor structure of the English version. The current studies addressed this need and tested the predictive and convergent validity of the ACS subscales. In Study 1, exploratory factor analysis yielded a two-factor model with Focusing and Shifting subscales. In Study 2, confirmatory factor analysis supported this model and suggested superior fit compared to the factor structure of the Icelandic version (Ólafsson et al., 2011). Study 3 examined correlations between the ACS subscales and measures of working memory, anxiety, and cognitive control. Study 4 examined correlations between the subscales and reaction times on a mixed-antisaccade task, revealing positive correlations for antisaccade performance and prosaccade latency with Focusing scores and between switch trial performance and Shifting scores. Additionally, the findings partially supported unique relationships between Focusing and trait anxiety and between Shifting and depression that have been noted in recent research. Although the results generally support the validity of the ACS, additional research using performance-based tasks is needed.

Music therapy with moderate Alzheimer's disease in a long-term care center

there was a three-way interaction between task type, switch, and group (p1⁄4 .022): supervets responded faster than controls when switching from the harder color-naming trials to the easier word-naming trials. Whereas controls showed a reaction time cost on these switch trials, supervets showed no reaction time cost. Conclusions: Our results suggest that supervets with many years of high-intensity exercise do not demonstrate robust cognitive benefits from this exercise regime, in comparison with matched controls. Where differences exist, they do not systematically favor the ’supervets’. Further study is needed to determine why long-term exercise regimes may not advantage cognition. One possibility is that long-term highintensity PA affects neuromodulators in ways that offset the advantageous effects seen with short-term exercise.

Withdrawal Symptoms and Rebound Syndromes Associated with Switching and Discontinuing Atypical Antipsychotics: Theoretical Background and Practical Recommendations

With the widespread use of atypical or second-generation antipsychotics, switching treatment has become current practice and more complicated, as the pharmacological profiles of these agents differ substantially despite their similarity in being 'atypical'. All share the ability to block dopamine D₂ receptors, and most of them also block serotonin 5-HT2A receptors. Apart from these common features, some atypical antipsychotics are also able to block or stimulate other dopamine or serotonin receptors, as well as histaminergic, muscarinergic or adrenergic receptors. As a result of the varying receptor affinities, in switching or discontinuing compounds several possible pitfalls have to be considered, including the occurrence of withdrawal and rebound syndromes. This article reviews the pharmacological background of functional blockade or stimulation of receptors of interest in regard to atypical antipsychotics and the implicated potential withdrawal and rebound phenomena. A MEDLINE search was carried out to identify information on withdrawal or rebound syndromes occurring after discontinuation of atypical antipsychotics. Using the resulting literature, we first discuss the theoretical background to the functional consequences of atypical antipsychotic-induced blockade or stimulation of neurotransmitter receptors and, secondly, we highlight the clinical consequences of this. We then review the available clinical literature on switching between atypical antipsychotics, with respect to the occurrence of withdrawal or rebound symptoms. Finally, we offer practical recommendations based on the reviewed findings. The systematic evaluation of withdrawal or rebound phenomena using randomized controlled trials is still understudied. Knowledge of pharmacological receptor-binding profiles may help clinicians in choosing adequate switching or discontinuation strategies for each agent. Results from large switching trials indicate that switching atypical antipsychotics can be performed in a safe manner. Treatment-emergent adverse events during or after switching are not always considered to be, at least in part, associated with the pre-switch antipsychotic. Further studies are needed to substantiate the evidence gained so far on different switching strategies. The use of concomitant medication, e.g., benzodiazepines or anticholinergic drugs, may help to minimize symptoms arising from the discontinuation or switching of antipsychotic treatment.

Sustained and transient attentional processes modulate neural predictors of memory encoding in consecutive time periods

Memory formation is commonly thought to rely on brain activity following an event. Yet, recent research has shown that even brain activity previous to an event can predict later recollection (subsequent memory effect, SME). In order to investigate the attentional sources of the SME, event-related potentials (ERPs) elicited by task cues preceding target words were recorded in a switched task paradigm that was followed by a surprise recognition test. Stay trials, that is, those with the same task as the previous trial, were contrasted with switch trials, which included a task switch compared to the previous trial. The underlying assumption was that sustained attention would be dominant in stay trials and that transient attentional reconfiguration processes would be dominant in switch trials. To determine the SME, local and global statistics of scalp electric fields were used to identify differences between subsequently remembered and forgotten items. Results showed that the SME in stay trials occurred in a time window from 2 to 1 sec before target onset, whereas the SME in switch trials occurred subsequently, in a time window from 1 to 0 sec before target onset. Both SMEs showed a frontal negativity resembling the topography of previously reported effects, which suggests that sustained and transient attentional processes contribute to the prestimulus SME in consecutive time periods.

Switch probability context (in)sensitivity within the cognitive control network

Cognitive control processes refer to the ability to flexibly adapt one's thoughts and actions in the pursuit of an internal goal. Task preparation is a central aspect of cognitive control and has generally been studied using explicitly cued task-switching paradigms. Over the last decade, numerous fMRI studies have identified a fronto-parietal network to exhibit greater activity during the preparation of task switches than during the preparation of task repetitions, which is assumed to reflect endogenous cognitive control processes. There is, however, a huge variability in preparatory switch-specific brain activity reported in the imaging literature on task-switching. One factor that might explain this heterogeneity is the difference in switch probability across studies. In the current fMRI study, we examined which preparation-related cognitive control areas are susceptible to such contextual differences by manipulating the switch probability within subjects. In the low switch probability (30% switch trials) blocks, we found the frequently observed switch-related preparatory activation in fronto-parietal areas. In the high switch probability (50% switch trials) blocks, however, only part of these areas (more particularly the (pre-) SMA, extending into the dorsal ACC and the superior parietal lobule) showed higher activation in switch compared to repeat trials. The activation levels in the other areas (the lateral prefrontal cortex, inferior parietal lobule and middle temporal gyrus) were very similar for switch and repeat trials. Our results suggest a functional dissociation within the cognitive control network with some brain areas being sensitive to the switch probability context while others are not.